The future wireless communication is expected to meet communication demands of users anytime and anywhere, and this vision gradually becomes achievable along with the remarkable progress of mobile devices and wireless networks. To support ubiquitous communication services in different coverage scales, the wireless networks may include small-area and wide-area wireless networks. The small-area wireless networking technologies (e.g. WLAN, WPAN, micro-cellular) enable local or hotspot services. On the other hand, wide-area wireless network (e.g. macro-cellular) infrastructures established by mobile operators provide services to subscribers in large areas. The small-area and wide-area wireless networks can be integrated together to provide complementary and new services to end users in different locations. Therefore, the evolution leads to a networking environment of integrated heterogeneous networks where multiple wireless networks coexist geographically to support a variety of global ubiquitous services.
In such a wireless networking environment, traffic loads of different wireless networks will change in space and time because of unequal user densities and traffic activities; therefore, Radio Resources Management (RRM), and particularly, spectrum management should be able to provide more efficient utilization of limited radio resources.
The conventional strategy of fixed spectrum management is to issue a spectrum license to a specific Radio Access Technology (RAT) to enable the specific RAT to occupy the spectrum exclusively. However, such a manner of spectrum management is unable to adapt to the changing of spectrum demands dynamically in space and time, and it hence leads to uneven spectrum utilization and artificial spectrum shortage. Therefore it is essential to improve the efficiency of spectrum usage, and achieve more intensive spectrum utilization by spectrum sharing technologies.